Developments in Iraq on Sunday

* The U.S. ambassador to Iraq acknowledged serious problems ahead of next weekend's election but gave assurance Sunday that "great efforts" were being made so every Iraqi can vote.

* In an audiotape posted on the Web, a speaker claiming to be Iraq's most feared terrorist declared "fierce war" on democracy, raising the stakes in the vote. A speaker identifying himself as Abu Musab al-Zarqawi -- the leader of Iraq's al-Qaida affiliate -- condemned the election, branding candidates as "demi-idols" and saying those who vote for them "are infidels" -- a clear threat to the safety of all those who participate in the balloting.

* Rebels who have vowed to disrupt the balloting blew up a designated polling station near Hillah south of Baghdad and stormed a police station in Ramadi west of the capital, authorities said.

* To encourage as big a turnout of Sunnis as possible, U.S. and Iraqi troops have stepped up security operations in Baghdad, Mosul and other tense areas, rounding up hundreds of suspected insurgents. The U.S. command announced Sunday it had arrested an undisclosed "top insurgent suspect" in Baghdad after hunting him for nearly a year.

* A major insurgent group, the Ansar al-Sunnah Army, posted a videotape Sunday on a Web site showing the assassination of an Iraqi army colonel captured in Mosul. The tape showed a man in civilian clothes holding a military identification card. As the man sat in a chair, a masked gunman approached from his right and shot him in the head with a rifle. Another video posted on the Internet Sunday purportedly showed the shooting death of a captive Egyptian truck driver. A masked gunman shot him with three rounds in the back in daylight on a street corner as traffic passed by.

* The Chinese Foreign Ministry confirmed Sunday that eight Chinese construction workers taken hostage by Iraqi insurgents have been safely transferred to Chinese custody. A day earlier their captors said they were releasing the men.